The present invention relates to a device and a method for performing a gamma correction process on image signals for a liquid crystal display device such as a liquid crystal display projector.
A liquid crystal display device such as liquid crystal display (LCD) projector is widely used to enlarge and project an image such as computer screen image on a projector screen to perform a presentation or the like. In an LCD projector, signal processing such as digital conversion is performed on image signals provided to the LCD projector from an external device (e.g., computer). The LCD projector includes LCD panels and LCD drivers for respectively driving the LCD panels by generating an appropriate drive voltage based on processed image signals and applying the appropriate drive voltage to each display segment in the LCD panels. The LCD projector further includes a light source that emits light beam towards the LCD panels. The light is transmitted through images formed on the LCD panels to generate red, green, and blue image lights. A prism combines the three image lights to generate color image light. The LCD projector includes a projection lens for focusing the color image light on a projector screen so as to display an enlarged image on the projector screen.
A single liquid crystal display device includes a plurality of (normally three) LCD panels. Each LCD panel may have a different light transmission characteristic (hereinafter referred to as “V-T characteristic”) with respect to the drive voltage. This results in a difference in contrast ratio between LCD panels. To reduce the difference in contrast ratio, the signals provided to the LCD panel undergo a known correction (gamma correction). Gamma correction is described in, for example, Japanese Laid-Open Patent Publication No. 2004-212605 (IPC: G09G 3/36). In the gamma correction described in the publication, various types of gamma correction data are provided in advance in correspondence with the relationship between the contrast values of the three LCD panels. The V-T characteristics of the three LCD panels are measured with an illuminometer in a state in which gamma correction process is not performed. The V-T characteristic values measured by the illuminometer are provided to the microcomputer and compared with the relationship of the contrast values of the three LCD panels. An optimum gamma correction datum is selected from a plurality of gamma correction data for different characteristics in accordance with the comparison result. Three correction values respectively corresponding to the three LCD panels are calculated from the selected gamma correction datum. The signal (drive signal) provided to each LCD panel is corrected with the corresponding correction value.